Ch. 22: Nuclear Chemistry• Nuclear forces, and

radioactive decay• Alpha, beta, and gamma p

articles• Transmutation,

disintegration series, & carbon dating

• Fission vs. fusion• Effects of radiation

San Onofre Nuclear Power PlantSan Clemente, CA

(61 miles south of Los Angeles)

Chemical reaction vs. Nuclear reaction

Chemical reactions:• Atoms attain stable isotopes

by losing or sharing electrons

• Reactions affected by changes in temperature, pressure, or the presence of catalysts

Nuclear reactions:

• The nuclei of unstable isotopes gain stability by undergoing changes

• The changes are accompanied by emission of large amounts of energy

Nuclear chemistry: the chemistry of radioactive substances; study of the atomic nucleus, including fission and fusion and their products

The Nucleus

• Atomic nuclei are made of protons and neutrons, which are collectively called nucleons

• In nuclear chemistry an atom is referred to as a nuclide and is identified by the number of protons and neutrons in its nucleus.

• Two types of notations: Radium-228 or 228Ra 88

Nuclear Reaction• a reaction that affects the nucleus of an atom.• Occurs to increase stability• Give off large amounts of energy• Total of atomic #s & mass #s is equal on both

sides of equation.• Identity of atom does not change till atomic #

changes, When atomic #changes, the identity of element changes=transmutation

Natural Radioactivity Discovered in 1896 by Antoine Henri Becquerel, who saw a

uranium salt produce an image on a photographic film. The term radioactivity was coined in 1898 by Marie Curie, a

Polish physicist, who was doing research with her husband Pierre. (They did much of the initial work on radioactivity, and eventually died of radiation-related illnesses.)

Radioactive Decay: spontaneous disintegration of a nucleus into a slightly lighter & more stable nucleus, accompanied by emission of particles, electromagnetic radiation or both.

What determines the type of decay a radioisotope undergoes?

The nuclear force is an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleusAt these short distances, the nuclear force dominates over electromagnetic repulsions and hold the nucleus together.

More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These nuclei are in a region called the band of stability.

Types of Radioactive DecayType Consists of Stopped

byInteresting

Fact1.

alpha

He nucleus:2 p & 2 n

Paper or skin

If ingested, is harmful to lungs

2. beta

High energy e- Clothing, glasses, or thin sheet of Al

Causes damage to sensitive tissues like eyes

3. gamma

Photon (particle of light)* Has essentially no mass (m < 5.81 x 10-72 g…its complicated!)

A few feet of dirt or concrete, or 6” of Pb

Causes severe damage to body tissues

• Alpha particle emissions:– Helium nucleus: 2 protons and 2

neutrons, +2 charge.– For large, unstable nucleus which

needs to reduce both the number of protons and the number of neutrons.

– Example:

HePbPο 42

20682

21084

• Alpha emission

• Beta particle emissions:– Electron emission, -1 charge.– For unstable nucleus which needs to

reduce the number of neutrons.– A neutron is converted into a

proton and an electron, the electron is given off as a beta particle.

– Example:βNC 0

1147

146

• Beta emission

Some of the tiny particles that exist and transform in nuclear reactions have various names such as neutrinos and quarks. This can lead to the discussion of matter and antimatter.

11

• Positron emissions:– Positron emission, +1 charge.– For unstable nucleus which needs to

reduce the number of protons.– A proton is converted into a neutron

and a positron, the positron is emitted.

– Example:βBC 0

110

510

6

• Electron capture:– An inner orbit electron combines with a proton

and forms a neutron.– For unstable nucleus which needs to reduce the

number of protons.– Example:

LieBe 73

01

74

• Electron capture

• Gamma emissions:– High energy electromagnetic waves

(photons) like visible light, except with a shorter wavelength.

– For high energy nucleus when it jumps down from an excited state to a ground state.

– Example:

γHeHe 32

32

• Gamma emission

17

1. Using the examples above, write the reaction of bismuth-214 emitting an alpha particle

2. Write the reaction of silicon-27 emitting a beta particle

HeTlBi 42

21081

21483

ePSi 01

2715

2714

Half Life: The time required for ½ the amount of a

radioactive material to disintegrate.

• Phosphorus-32 radioactively decays to form Sulfur-32

• Half life 32P = 14 days

Time amount

0 hours 1.0 mg

2.6 hours 0.5 mg

5.2 hours 0.25 mg

7.8 hours 0.125 mg

10.4 hours 0.0625 mg (6.25x10-5 g)

Arificial Transmutation• First accomplished by Rutherford in 1919, even though alchemists

tried for hundreds of years.• Transmutation of lead into gold was achieved by Glenn Seaborg,

who succeeded in transmuting a small quantity of lead in 1980. He also first isolated plutonium for the atomic bomb and discovered/”created” many elements. (NY Times, Feb 1999)

• There is an earlier report (1972) in which Soviet physicists at a nuclear research facility in Siberia accidentally discovered a reaction for turning lead into gold when they found the lead shielding of an experimental reactor had changed to gold.

• Accomplished with particle accelerators like the Stanford Linear Accelerator (SLAC)

Disintegration Series (Decay Series)• “Heavy” atoms (greater than Bismuth, #83) naturally decay to

smaller atoms along a consistent path, or series, of decays.

Radioactive U-238 → Th-234 + Th-234 → Pa-234 + Pa-234→ U-234 + U-234→ Th-230 + Th-230 → Ra-226 + Ra-226 → Rn-222 + Rn-222 → Po-218 + Po-218 → Pb-214 + Pb-214 → Bi-214 + Bi-214 → Po-214 + Po-214 → Pb-210 + Pb-210 → Bi-210 + Bi-210→ Po-210 + Po-210 → Stable Pb-206 +

Mass

Nu

mb

er

Atomic Number & Symbol

Source: http://www.frontiernet.net/~jlkeefer/uranium.html

Nuclear Fission • Fission: process in which the nucleus of a large, radioactive atom

splits into 2 or more smaller nuclei– Caused by a collision with a energetic neutron.

• A neutron is absorbed by a U-235 nucleus. The nucleus is now less stable than before. It then splits into 2 parts and energy is released. Several neutrons are also produced; they which may go on to strike the nuclei of other atoms causing further fissions.

Fission animation: http://www.howstuffworks.com/nuclear-bomb3.htm

Ba +13956 Kr +94

36 3 n + energy10 U235

92n + 10

• *In a fission reaction that is working properly, more than one neutron ejected from the fission reaction causes another fission to occur. This condition is known as supercriticality.

• *The process of neutron capture and nucleus splitting happens very quickly (takes about 1 x 10-12 seconds).

• An incredible amount of energy is released:– As heat and gamma radiation– Because the product atoms and neutrons weigh less than the

original U-235 atom; the “missing mass“ has been converted to energy by E=mc2

*A Fission Chain Reaction

Harnessing Fission: A nuclear power plant• Nuclear power plants utilize the energy released in a controlled fission reaction in the core to heat water in one pipe, which is used to vaporize water into steam in another pipe, which drives a turbine and generates electricity.

• The vaporized H2O is in a closed circuit, and is never exposed to the radiation itself.

• The speed of the fission chain reaction is regulated using carbon control rods which can absorb extra neutrons.

The Atomic Bomb• Uses an unregulated fission reaction in a very

fast chain reaction that releases a tremendous amount of energy.

*Critical mass: the minimum amount of radioactive, fissionable material needed to create a sustainable fission chain reaction

* Site of fission reaches temperatures believed to be about 10,000,000°C.

• Produces shock waves and , , , x-rays, and UV radiation.

US Army aerial photograph from 80 km away, taken about 1 hour after detonation over Nagasaki, Japan, August 9, 1945.

*The classic “mushroom cloud” is a result of dust and debris lifted into the air as a result of the

detonation.

Nuclear FusionFusion: process in which 2 nuclei of small elements are united to form

one heavier nucleus• Requires temperatures on the order of tens of millions of degrees

for initiation.• The mass difference between the small atoms and the heavier

product atom is liberated in the form of energy.• Responsible for the tremendous energy output of stars (like our

sun) and the devastating power of the hydrogen bomb.

H + 31

H

21

He +42

n10

+ energy

*Stars & the Hydrogen Bomb• The first thermonuclear bomb was exploded in 1952 in the

Marshall islands by the United States, the second was exploded by the Russia (then the USSR) in 1953.

• “H bombs” utilize a fission bomb to ignite a fusion reaction.

Cold fusion

• Martin Fleischmann and Stanley Pons• 1989• Univ. of Utah• Cold fusion lie

Mass-Energy Relationship• *The energy that can be released from 2 kg of

highly enriched U-235 (as used in a nuclear bomb) is roughly equal to the combustion of a million gallons of gasoline. 2 kg of U-235 is smaller than a baseball; a million gallons of gasoline would fill a rectangular tank that is 50 feet per side.

Measurement of Radioactivity

ionizing radiation-• radiation from radioactive sources• When it strikes an atom or a molecule, one or more

electrons are knocked off and an ion is created• Measured with a Geiger counter, film badge or a

Scintillation counter• Curie-measures radioactivity emitted by a radionuclide.• Roentgen & Rad - measures exposure to gamma rays or

X-rays• Rem- takes into account the degree of biological effect

caused by the type of radiation exposure.

*Biological Effects of Radiation: Acute• High level radiation (gamma ray & x–ray) causes death• Damage centered in the nuclei of the cells; cells that are undergoing

rapid cell division most susceptible • Gamma rays from a Co-60 source are often used to treat cancer

(cells that multiply rapidly)

Ionizing radiation: energy emitted from radioactive matter; it can directly affect (ionize) the structure of materials which it passes through, including human tissue.

Long term exposure can weaken an an organism and lead to onset of malignant tumors, even after fairly long time delays.Largest source: X–raysSr-90 isotopes are present in fallout from atmospheric testing of nuclear weapons.

Contaminated foods can increase incidence of leukemia and bone cancers.

*Effects of Radiation: Long Term